Maintaining the position of a subject while performing acts upon the subject can be of critical importance in certain circumstances. In the medical field, for example, during certain treatment procedures (e.g., radiation therapy procedures) it can be critical to effective treatment and safety that the area designated for treatment be positioned correctly and remain in place during the procedure. Incorrect initial positioning as well as excessive movement of the patient subject and associated target area designated for treatment without adjustment may result in the application of radiation to areas beyond the designated target area, in turn resulting in potentially ineffective, even harmful, treatment of the patient subject. Other medical treatment regimes and procedures, e.g., radiation therapy simulations and stereo tactic radio surgery, similarly call for the accurate targeting of areas upon the subject to insure accuracy, safety and effectiveness. Some methods which attempt to address these concerns are dependent upon mechanical measurement devices or retro reflective objects and surfaces to improve reflected signal strength to the signal receiver, while others which employ optical or sonic time-of-flight measurement techniques may not achieve the desired accuracy (e.g., margins of error of less than 1 mm at distances up to 5-7 meters).
A need thus exists for relatively simple yet effective and accurate apparatus and methods for maintaining the spatial position of a target area during application of medical treatment or during the performance of other acts upon a subject.